The invention relates to radial ply pneumatic tires.
It is a continuing goal in the art to reduce tire weight, and the amount of material in a tire without reducing performance characteristics. In the past, attempts have been made to reduce the number of carcass plies used in passenger tires from two plies to one ply by using larger and stronger carcass ply reinforcement cords. Although such monoply tires perform as well as the two ply tires for many tire properties, such monoply tires have shown major distortion in the areas of the tire coinciding with overlap splices. Apparently, in a two-ply tire the plies support each other and such distortion is not a major problem.
The challenge in producing a monoply tire, therefore, is to find materials or a tire construction that is not susceptible to such distortions, while other properties are maintained.
A pneumatic tire of the invention comprises a pair of parallel annular beads, a single carcass ply comprising poly(ethylene 2-6 naphthalene dicarboxylate) reinforcement cords wrapped around the beads, a belt package disposed radially outward of the carcass ply in a crown area of the tire, tread disposed radially outward of the belt package, and sidewalls disposed between the tread and the beads. The PEN reinforcement in the carcass ply comprises 2000 to 8000 dTex cords having a twist multiplier of 5 to 10, said cords showing a shrinkage of 2.5% to 7%, a LASE @ 5% of 85 to 115 N. a break strength of 200 to 350 N, a 90% to 100% Retained break strength based on the Dynamic Flex Fatigue test, and a cord density of 20 to 40 ends per inch (e.p.i. measured at tire bead).
In an illustrated embodiment, the reinforcement in the carcass ply comprises 1100/1/3 dTex PEN cords with a 394 turns per meter Zxc3x97394 turns per meter S twist, said cords showing a 3.2% shrinkage, 99 N LASE @ 5%, 252 N break strength, and 94% Ret BS Dynamic Flex Fatigue.
In the illustrated embodiment, the carcass ply is reinforced with 1100/1/3 PEN cords at a cord density of 26 to 30 e.p.i. (as measured at tire bead), said cords having an angle of 75xc2x0 to 90xc2x0 with respect to the equatorial plane of the tire.